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Hi guys! Was hoping that someone here might have an idea of whats going on with my system, or maybe someone has had this issue before.
I have a ’91 Bronco and the Battery Voltage drops from 12.8v to 12.1 and sometimes even 11.9v over night. Used my Fluke to test for a Parasitic Battery Drain. Even had a friend check my results. My Parasitic Draw is ~175mA. The Battery is from O’reilly an I bought it approx. June 2017. I also replaced the Alternator in July 2017 went from a Ford 2g alt to a Ford 3g unit. I have replaced both the positive and negative battery cables.
I have had the battery tested at O’Reilly’s and it passes the CCA test, and the Alternator passes the charging test. Alternator puts out 14.3v no load and 13.6 with the blower on high and the High-beams on.
The only thing that I can think of is that the internal resistance in the battery is high and is causing it to drop over night. even when the battery is at 11.5 or 11.3v that starter still turns good and strong.
Any help is welcome. Thanks.
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175mA is way too much draw.
Follow ETCG testing , etc. here:
https://www.ericthecarguy.com/faq/solving-automotive-electrical-problems/parasitic-draw-testingDon’t overlook the fact that a defective diode in an alternator can drain battery power while the car is parked.
Either test as directed in the link or just disconnect the alternator battery power lead before parking it overnight and see if the charge is OK in the AM.Oh whoops, I thought I could keep it under 200mA. Ok, let me check my After Market wiring I have done recently and see what needs to be moved to a ignition 12v circuit. I currently have a charger on the battery so I will check my draw again after work today.
It is not uncommon for modern vehicle with all their computers to draw some current.
Nominally around 50 mA. after the systems go to “sleep”
To ensure the vehicle has gone to “sleep”
Any and all door and hood switches need to be in their closed positions.
It may take a few minutes to as much as an hour for the vehicle to reach that state.
Using a DVOM.
You can watch the current draw drop as the vehicle systems go to sleep.Ford was still running a basic computer in 1991. Once you rotated your ignition to the off position the computer was done and off.
It started raining hard here when I was getting off work so I left the battery on the charger for the evening.
Could have a cell in battery starting to die check the diode in the alternator that I agree with bonnieman i have had a battery that tested good at AutoZone the next day took it back in and they had to replace it because it was actually bad but they had to do 3 different major tests before they found out it was failing the last test
Oh boy here we go, Looks like I inflicted my own wound. 🙁 I had a accessory that was wired straight to the battery. I thought it was only 175mA but it was almost half a amp. I moved the accessory over to a 12v source that comes on and off with the vehicle’s ignition switch and now my Draw is only 4mA.
I had forgot’n about this accessory because it had been plugged into my Bronco for so long that the only reason that I started noticing it now is that I only drive that Bronco every 2-3days. According to my rough math with a 500mA draw and a 35-40Ah battery I had 3 to 3.5days before my battery would be dead. But driving the vehicle everyday I would never notice the issue. Glad this fix was didn’t require a new alternator.
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